The ERF gene was initially identified on the basis of its ability to bind to the ETS-specific DNA response element sequence, and was later shown to act as a suppressor of ETS-responsive promoters in transient transfection assays. Experiments were performed to test whether ERF can inhibit the expression of retroviruses whose promoters contain ETS- responsive elements and which, in transient assays, can be shown to be inhibited by ERF. It has been shown that in cells co-transfected or co- infected with a murine leukemia virus (MuLV)-derived viral construct and ERF, the level of viral RNA expression is reduced in comparison to control cells containing vector sequences only. These results suggest that ERF could potentially act as a virus inhibitor in vitro.